One anecdote sums up how Wall Street's workforce has changed since the financial crisis

There is an apocryphal anecdote about a chief executive of a
European bank and a trip to the trading floor that pretty much
sums up what has happened to Wall Street staffing since the
financial crisis.

The story goes like this: The bank had just cut a bunch of
traders, and the CEO happened to walk across the trading floor
where many of those staff once worked. To his surprise, the floor
still looked pretty full.

He turned to a colleague, and said something to the effect of:
"Who are all these people? I thought we just fired a bunch of
traders?"

His colleague responded by confirming that the bank had indeed
just fired a bunch of traders. Their seats had been taken by
compliance staff.

I have no idea if it is true, but it sums up one of the key
issues banks have faced since the financial crisis: While
front-office headcount and compensation have decreased,
back-office staffing and costs have gone up.

Back-office

I was reminded of the anecdote while reading through a JPMorgan
note on the banking sector. The table below shows how
investment-bank compensation expenses fell 21% from 2009 to 2015,
with this figure dropping 39% at Credit Suisse.

Noncompensation expenses (think bank infrastructure, IT, systems,
etc.) have increased, however, by 7%. And headcount has only
fallen 3%, despite huge cuts to the number of traders and bankers
at the banks.

JPMorgan

The JPMorgan analysts have a case study too, focusing on Deutsche
Bank. The number of front-office staff there fell from 10,085 in
2011 to 7,895, according to the analysts, yet the total number of
employees housed in corporate banking and securities remained
stable.

The ratio of infrastructure staff to front-office headcount
jumped from 1.7 to 2.4 over the same period.